Seismic response of base-isolated structures during impact with adjacent structures

The seismic response of multi-story building supported on various base isolation systems during impact with adjacent structures is investigated. The isolated building is modeled as a shear type structure with lateral degree-of-freedom at each floor. An impact element in the form of spring and dashpot is used to model the adjacent structure (i.e. retaining wall or entry bridge). The coupled differential equations of motion for the isolated system are derived and solved in the incremental form using Newmark’s step-by-step iteration method. The variation of top floor absolute acceleration and bearing displacement for different isolation systems during impact upon the adjacent structures under different earthquakes is computed to study the behavior of the building during impact and comparative performance of various isolation systems. The impact response of isolated building is studied under the variation of important system parameters such as size of gap, stiffness of impact element, superstructure flexibility and number of story of base-isolated building. It is concluded that the response of base-isolated structures is affected when impact takes place with the adjacent structures and hence need to be avoided. The superstructure acceleration increases and the bearing displacement decreases due to impact with adjacent structure. However, even after the occurrence of impact phenomenon, the isolation remained effective as compared to the non-isolated structure. Further, it is also observed that superstructure acceleration increases with the increase of the isolation gap up to a certain value and then the acceleration decreases with further increase of gap. The effects of impact are found to be severe for the system with flexible superstructure, increased number of story and greater stiffness of the adjacent structure.